Waveguide structure for guiding light in low-index material

Abstract

A high-index-contrast waveguide structure material used to guide light through a low-refractive-index material. In one embodiment, the waveguide structures are capable of guiding and confining light in such a way that very high optical intensity is obtained in a small cross-sectional area or gap filled with any material with sufficiently low refractive index, relative to the remainder of the structure. The structure may be used to form resonators, optical couplers, directional optical couplers and other optical devices. Structures may be formed consistent with integrated circuit forming processes.

1. A light guiding structure comprising:
 a pair of high refractive index regions spaced apart to form a nanometer order gap having a low refractive index adapted to operate as a waveguide by concentrating optical power in the gap and propagating the optical power along a length of the gap. 
 
     
     
       2. The light guiding structure of  claim 1  wherein the gap separates the high index regions by between approximately 10 nanometers and 200 nanometers. 
     
     
       3. The light guiding structure of  claim 1  wherein the high refractive index regions have an index of refraction of approximately at least 3.48, and the low refractive index gap has an index of refraction of approximately at most 1.46. 
     
     
       4. The light guiding structure of  claim 1  wherein the respective refractive indices provides strong optical confinement in the gap. 
     
     
       5. The light guiding structure of  claim 1  wherein the mode of light propagation comprises Eigenmodes. 
     
     
       6. The light guiding structure of  claim 1  and further comprising a cladding, covering surfaces of the high index regions. 
     
     
       7. The light guiding structure of  claim 1  wherein a high refractive index contrast between the high refractive index regions and the low refractive index gap provides an electric field discontinuity between the regions and strong light confinement and optical intensity in the low refractive index gap. 
     
     
       8. The light guiding structure of  claim 7  wherein the electric field where the high refractive index regions and low refractive index gap meet, is higher at the low-index side and lower at the high-index side, with an electric field ratio equal to the square of the index contrast (n High /n Low ) 2 . 
     
     
       9. The light guiding structure of  claim 1  wherein the low refractive index gap comprises a non-linear optical material. 
     
     
       10. A light guiding structure comprising:
 a substrate; 
 an insulating layer supported by the substrate; 
 a pair of high refractive index regions supported by the insulating layer and spaced apart to form a nanometer order gap having a low refractive index adapted to form a waveguide such that light is propagated along the gap; and 
 a cladding formed on top of the high refractive index regions. 
 
     
     
       11. The light guiding structure of  claim 10  wherein the cladding has a low refractive index. 
     
     
       12. The light guiding structure of  claim 11  wherein the gap contains cladding. 
     
     
       13. The light guiding structure of  claim 10  wherein a high refractive index contrast between the high refractive index regions and the low refractive index gap provides an electric field discontinuity between the regions and gap and strong light confinement and optical intensity in the low refractive index gap. 
     
     
       14. The light guiding structure of  claim 13  wherein the electric field where the high refractive index regions and low refractive index gap meet is higher at the low-index side and lower at the high-index side, with an electric field ratio equal to the square of the index contrast (n High /n Low ) 2 . 
     
     
       15. The light guiding structure of  claim 10  wherein the distance of the gap between high refractive index regions is smaller if high intensity is desired, and may be larger if more power in the low-index layer is preferred. 
     
     
       16. The light guiding structure of  claim 15  wherein the distance of the gap between high refractive index regions is smaller than the wavelength of optical waves to be transmitted in the gap. 
     
     
       17. The light guiding structure of  claim 15  wherein the thickness of the high-refractive-index layers is comparable to half of the wavelength. 
     
     
       18. The waveguide of  claim 10  wherein the gap comprises a non-linear optical material. 
     
     
       19. A light guiding structure comprising:
 a high refractive index region containing a nanometer order gap having a low refractive index; and 
 a low refractive index region around the high refractive index region such that light is propagated in the gap. 
 
     
     
       20. The waveguide of  claim 19  wherein the high refractive index region and gap are substantially circular in shape. 
     
     
       21. The waveguide of  claim 20  wherein the high refractive index region and gap are substantially concentric. 
     
     
       22. The light guiding structure of  claim 19  wherein a high refractive index contrast between the high refractive index region and the low refractive index gap provides an electric field discontinuity between the regions and gap and strong light confinement and optical intensity in the low refractive index gap. 
     
     
       23. The light guiding structure of  claim 19  wherein the gap comprises a non-linear optical material. 
     
     
       24. An optical resonator comprising:
 a pair of high refractive index regions spaced apart by a nanometer range low refractive index gap in a substantially circular shape, forming a continuous slot waveguide such that light is propagated in the gap. 
 
     
     
       25. The waveguide of  claim 24  wherein the mode of light propagation comprises Eigenmodes. 
     
     
       26. The waveguide of  claim 24  and further comprising a cladding, covering surfaces of the high index regions. 
     
     
       27. The waveguide of  claim 24  wherein a high refractive index contrast between the high refractive index regions and the low refractive index gap provides an electric field discontinuity between the regions and strong light confinement and optical intensity in the low refractive index gap. 
     
     
       28. The waveguide of  claim 27  wherein the electric field where the high refractive index regions and low refractive index gap meet, is higher at the low-index side and lower at the high-index side, with the ratio equal to the square of the index contrast (n High /n Low ) 2 . 
     
     
       29. The resonator of  claim 24  and further comprising a substantially straight waveguide positioned adjacent the circular high refractive index regions and optically coupled thereto. 
     
     
       30. The resonator of  claim 29  wherein the substantially straight waveguide comprises a slot waveguide. 
     
     
       31. A directional optical coupler comprising:
 a first slot waveguide having regions of high refractive index separated by a low refractive index gap that concentrates optical power in the gap; and 
 a second slot waveguide having regions of high refractive index separated by a low refractive index gap that concentrates optical power in the gap, wherein the first and second slot waveguides are substantially parallel and optically coupled for a desired distance, and wherein they diverge at at least one end. 
 
     
     
       32. An optical coupler comprising:
 two rails of high index of refraction material running substantially parallel and separated by a low refractive index gap that concentrates optical power in the gap, wherein the rails diverge into two laterally spaced apart tips, the tips separated by a distance adapted for mode matching with an optical fiber having larger dimensions than the rails. 
 
     
     
       33. A waveguide comprising:
 two rails of high index of refraction material running substantially parallel; 
 a pair of spacer rods positioned adjacent the rails, and separating the rails to form a gap of low index of refraction material that concentrates optical power in the gap. 
 
     
     
       34. The waveguide of  claim 33  and further comprising a low index of refraction cladding surrounding the rails. 
     
     
       35. The waveguide of  claim 1  wherein the pair of high refractive index regions run substantially parallel to each other to guide light in an Eigenmode propagation. 
     
     
       36. The waveguide of  claim 1  wherein the pair of high refractive index regions run substantially parallel to each other to guide light strongly confined along the gap. 
     
     
       37. The waveguide of  claim 10  wherein the pair of high refractive index regions run substantially parallel to each other to guide light in an Eigenmode propagation. 
     
     
       38. The waveguide of  claim 10  wherein the pair of high refractive index regions run substantially parallel to each other to guide light strongly confined along the gap.